1. Technical Field
An improved nutating pump is disclosed as well as control systems for nutating pumps and methods of controlling dispense rates of nutating pumps so as to prevent, on one hand, splashing, and, on the other hand, motor stalling. The nutating pumps, control systems and methods disclosed herein are applicable to the field of paint colorant dispensers but have numerous other applications as well.
2. Description of the Related Art
Paints are made in a vast number of different colors and shades of colors. Each specific paint color has a specific formula of components to provide the desired color. A paint formula generally includes a relatively large amount of a base and smaller amounts of one or more colorants. Each colorant is measured according to the formula and dispensed from a bulk colorant supply, added to the base, and then mixed to produce the desired paint color.
Existing colorant dispensers have been used in retail paint supply stores and hardware stores, for example. Existing colorant dispensing equipment has included manual and automated machines. Automated colorant dispensing equipment can include several bulk colorant containers, in which each colorant container is connected to an inlet of a fluid pump. The outlet of each fluid pump is typically connected to a three-way valve which has a dispense outlet connected to a dispense nozzle and a by-pass outlet connected to a recirculation fluid line. Either one motor may drive all pumps or several pumps may be driven by a single motor through a common drive mechanism or each pump may be driven by an individual motor.
In single motor systems, when an amount of colorant is dispensed, the motor drives the pumps and the three-way valve for the particular colorant is opened to allow the colorant to be dispensed through the nozzle. The time period that the valve remains open determines the amount of colorant dispensed. Also, the colorant recirculates back into its container rather than being undesirably dispensed. The other three-way valves, which may be simultaneously driven by the motor, are in a by-pass mode.
However, existing colorant dispensing equipment can be improved. Existing colorant dispensing equipment utilizes a three-way valve for each colorant container, which increases the equipment costs and manufacturing costs. Also, the plurality of three-way valves tend to be a significant source of maintenance and service problems. Furthermore, the accuracy of the amount of colorant dispensed using the existing pump and valve arrangements can be improved. Also, a by-pass colorant flow path is needed because of the prominence of using a single motor to simultaneously operate all of the pumps. It is desired to more accurately control the amount of colorant dispensed so that the resulting paint color for any particular formula is more consistent. Greater accuracy and control over the colorant dispensing process provides greater consistency in paint color for any given formula.
One paint colorant dispenser disclosed in copending application Ser. No. 09/665,695 utilizes a nutating pump and a computer control system to control the pump. Nutating pumps have a piston which is positioned inside of a housing having a fluid inlet and a fluid outlet. The piston simultaneously slides axially and rotates inside of the housing. Prior to the system disclosed in application Ser. No. 09/665,695, existing nutating pumps have been operated by rotating the piston through a full 360xc2x0 rotation and corresponding axial travel of the piston. Such piston operation results in a specific amount of fluid pumped by the nutating pump with each revolution. Accordingly, the amount of fluid pumped for any given nutating pump is limited to multiples of the specific volume. If a smaller volume of fluid is desired, then a smaller sized nutating pump is used or manual calibration adjustment are made to the pump.
For example, in the art of mixing paint, paint colorants can be dispensed in amounts as little as {fraction (1/256)}th of a fluid ounce. As a result, existing nutating pumps for paint colorants can be very small. With such small dispense amount capabilities, the motor of such a small pump would have had to run at excessive speeds to dispense larger volumes of colorant (multiple full revolutions) in an appropriate time period.
In contrast with larger pumps, in order to minimize the dispense motor speed, a partial revolution dispense for such a larger capacity nutating pump would be advantageous. However, using a partial revolution to accurately dispense fluid is difficult due to the non-linear output of the nutating pump dispense profile vs. angle of rotation.
Specifically, typical nutating pumps have a sinusoidal dispense rate or flow rate profile. Referring to FIG. 1, this sinusoidal profile is graphically illustrated. The line 1 graphically illustrates the flow rate at varying points during one revolution of the piston. The portion of the curve 1 above the horizontal line 2 representing a zero flow rate represents the output while the portion of the curve 1 disposed below the line 2 represents the intake. Both the pump output and pump intake flow rates reach both maximum and minimum levels and therefore there is no linear correlation between piston rotation and either pump output or pump intake. The disclosure of application Ser. No. 09/665,695 addresses this problem by dividing a single revolution of the pump piston into a plurality of steps that can range from several steps to four hundred steps or more. Controllers and algorithms are used with a sensor to monitor the angular position of the piston, and using this position, calculate the number of steps required to achieve the desired output. Various other improvements and methods of operation are disclosed in the application Ser. No. 09/665,695.
The sinusoidal profile illustrated in FIG. 1 is based upon a pump operating at a constant motor speed. While operating the pump at a constant motor speed has its benefits in terms of simplicity of controller design and pump operation, the use of a constant motor speed also has inherent disadvantages which are illustrated in FIG. 1. Specifically, in certain applications, the maximum output flow rate illustrated on the left side of FIG. 1 can be disadvantageous because the output fluid may splash or splatter as it is being pumped into the output receptacle at the higher flow rates. For example, in paint mixing applications, any splashing of the colorant as it is being pumped into the output pail results in an inaccurate amount of colorant being deposited in the pail but also colorant being splashed on the colorant machine which requires labor intensive clean-up and maintenance. Obviously, this splashing problem will adversely affect any nutating pump application where precise amounts of output fluid are being delivered to an output receptacle that is either full or partially full of liquid or small output receiving receptacles. Paint colorant systems are but one example where splashing will be problematic.
Further, in addition to the splashing problem discussed above, the large pressure drop that occurs within the pump as the piston rotates from the point where the dispense rate is a maximum to the point where the intake rate is a maximum (i.e. the peak of the curve shown at the left of FIG. 1 to the valley of the curve shown towards the right of FIG. 1) can result in motor stalling for those systems where the motor is operated at a constant speed. As a result, motor stalling will result in an inconsistent or non-constant motor speed, there by affecting the sinusoidal dispense rate profile illustrated in FIG. 1, and consequently, would affect any control system or control method based upon a preprogrammed sinusoidal dispense profile. The stalling problem will occur on the intake side of FIG. 1 as well as the pump goes from the maximum intake flow rate to the maximum dispense flow rate.
Accordingly, there is a need for approved nutating pump with approved control system and/or a method of control thereof where by the pump motor is controlled so as to reduce the likelihood of splashing during the dispense portion of the piston revolution and which can eliminate the possibility of any motor stalling as the piston rotates from a dispense position to an input position and vice versa.
Improved nutating pumps, control systems and methods of controlling such pumps are disclosed which accurately, consistently, and effectively dispense fluid. While the disclosed pumps and control systems are described in connection with paint colorant dispensers, the disclosed pumps and control systems can be utilized to dispense any desired fluid. For example, the disclosed pumps and control systems and methods can be used in fluid dispensers for pharmaceuticals, cosmetics, inks, and other fluids at controlled volumes.
A disclosed paint colorant dispenser has a computer control system which operates a stepper motor or other incrementally controlled drive that drives a valveless pump, such as a nutating pump. Paint color formulas are stored in the computer control system and selected by an operator to mix a desired color of paint. The nutating pump pumps colorant from a bulk container to a dispense nozzle based on signals sent by the computer control system according to the paint color formula. The computer control system operates the stepper motor and the nutating pump such that the pump piston rotates less than a full 360xc2x0 revolution for each step of the stepper motor. For example, 400 steps may be required for one fill 360xc2x0 revolution. The stepper motor and the nutating pump are rotated through a desired number of steps to dispense a desired amount of fluid.
In addition to breaking down a piston rotation into a plurality of steps, the control system also acts to reduce the motor speed during those steps of the profile where the dispense rate is highest (i.e. the peak of the sinusoidal dispense profile) which reduces the possibility of splashing and therefore an inaccurate dispense of fluid. In an embodiment, the control system may also increase the motor speed during the intake portion of the profile. The speed can be increased during the intake in a variety of ways. One embodiment would involve increasing the motor speed during the beginning and end portions of the intake to increase the intake flow rate at the beginning and end portions of the intake without increasing the peak intake flow rate.
Another embodiment involves a uniform increase of motor speed during the intake portion of the cycle which would, of course, increase the peak intake flow rate. An advantage of increasing motor speed during the intake portion of the profile would be to make up for lost time which results from reducing the peak dispense rate during the dispense portion of the profile. Of course, other embodiments would include reducing motor speed and peak dispense rate during the dispense portion of the profile without modifying the intake portion of the profile.
The nutating pump of the present invention can be adjustable. For example, the angle between the axis of the nutating pump piston and the axis of the stepper motor shaft can be adjusted by an actuator. The computer control system sends signals to the actuator to operate the actuator which positions the nutating pump piston at a desired angle. The automated nutating pump angle adjustment effectively adjusts the pump fluid output through computer control.
Another nutating pump adjustment also provides for changing the pump fluid output. In this adjustment, the distance that a spherical bearing is off-set from the stepper motor shaft can be varied. For example, the bearing off-set adjustment alters the fluid output of the nutating pump, and can be used to calibrate the pump.
Various advantages of the disclosed pumps, control systems and control methods will become apparent upon reading this disclosure including the appended claims with reference to the accompanying drawings. Certain advantages may be desired, but not necessarily required to practice the principles embodied in this disclosure.
It will also be noted that the control methods disclosed herein apply to pumps other than nutating pumps.